This invention relates generally to chemical mechanical polishing (CMP) of wafers, and more particularly to the closed loop control of a CMP station using data from an inline metrology device.
A challenging and necessary step in wafer processing is planarization of the wafer's surface after forming a layer of the integrated circuit. Fabricating integrated circuits on a wafer can begin with etching the wafer's dielectric material to create a patterned surface. In the trenches of the dielectric patterns is where the conductive features will be formed. A conductive material, such as copper, is then layered over the patterned surface. This step of layering copper onto the patterned surface of the wafer creates an irregular wafer profile. The wafer must be planarized to eliminate metal residue on the dielectric so that no current leakage occurs. Further, if a subsequent layer of the integrated circuit is to be formed, the wafer's surface must be sufficiently planar. One method of planarizing the wafer surface is by using CMP.
A CMP station mounts the wafer at a polishing station and polishes the wafer by moving it across or around a polishing pad. A polishing slurry is used in conjunction with the pad. The slurry contains at least one chemically-reactive agent and can contain abrasive particles. The CMP station can house multiple polishing stations. Each polishing station can employ distinct polishing parameters, conditions, and techniques such as polishing slurries, pad surfaces, applied pressures, polishing time, and metrology devices. In some CMP stations, the first polishing station polishes down the copper layer. The subsequent polishing stations then polish away the barrier material and any copper that is not part of the copper features of the integrated circuit. Underpolishing the wafer leaves copper and barrier material on the dielectric of the wafer and leads to current leakage. Overpolishing wears away too much of the copper features increasing resistance and nonuniform conductivity of the integrated circuits.